Ketoacids, esters

A similar effect could be observed when we investigated the reduction of 3-ketoacid esters by Saccharomy-ces cerevisiae and the hydrolysis of 3-acetoxyacid esters by Candida utilis (17). As shown in Figure 4 the chiral... 

The configuration of 3-hydroxyacid esters obtained by yeast reduction of 3-ketoprecursors depends on the chain length of the acids (.18. >1.9). Zhou et al. (20)demonstrated that the structure of the alcohol esterified in 3-ketoacid esters also influences the configuration of the 3-hydroxycompounds that are formed. The fact, that the optical purity of the products depends on the concentration of the 3-ketocompounds (21) indicates the presence of competing enzymes leading to opposite enantiomers at different rates. 

Figure 4. Enantiomeric composition of 3-hydroxyacid esters formed by reduction of 3-ketoacid esters (baker s yeast) and hydrolysis of 3-acetoxyacid esters (Candida utilis).

Ethyl 3-hydroxybutanoate, isolated from yellow passion fruit, mainly consisted of the (S)-enantiomer (82 %), comparable to the product, obtained by yeast reduction of the corresponding 3-ketoacid ester (see above). In contrast, ethyl 3-hydroxybutanoate in purple passion fruit and mango mainly consisted of the (R)-enantiomer (69 % and 78 %). 

Birkenmeier, G. Birkenmeier, M. Huse, K. Use of a-ketoacid ester glyoxalase inhibitors for inhibiting cell proliferation and for the prevention and treatment of parasitic diseases. Ger. Often. DE 102005018642, 2006 Chem. Abstr. 2006,145, 410624. 

Trost and Salzmann 168) were able to stereoselectively introduce an E double bond by their sulfenylation-dehydrosulfenylation method (Scheme 64). Palladium catalyzed telomerization of butadiene (358) by Tsuji et al. 169) afforded diene (360) (Scheme 65). Ketoacid ester (363), obtained by terminal olefin oxidation and subsequent reduction, was treated with diphenyldiselenide and the resultant phenylselenyl group oxidatively removed to give the E a,P-unsaturated keto ester (365). 

In addition to /3-diketones, /3-ketoacids and /3-ketoesters, cyanoacetic ester and related compounds are suitable starting materials. The arylhydrazones 4 thus obtained are of great importance as starting materials for the Fischer indole synthesis, as well as for the preparation of other iV-heterocycles. ... 

The 9,10-phosphonostearic acid in form of its sodium salt shows a good thermal stability and was efficient as an inhibitor in rust protection. The diethyl-phosphonoacetoxystearic acid methyl ester is used as additive in high-pressure lubricants. Rust protection properties are also shown by 9,10-phosphonostearyl alcohol [157]. Trisodium 9,10-phosphonostearate possesses the best surface activity in an 0.2% aqueous solution showing 33 mN/m at 30°C and a pH value of 10.5 [156]. By the addition of dialkyl phosphite to a,p-unsaturated ketones the y-oxophosphonic acids are available [159]. Addition of dialkyl phosphite to y-ketoacids leads to a-hydroxy-y-carboxyphosphonates see Eq. (86) ... 

Photo-oxidation of protoporphyrin IX and its dimethyl ester Norrish type II reaction of amphiphilic ketoacid Quenching of naphthalene fluorescence by Ni2 +... 

This means that a reverse Claisen reaction can occur if a P-ketoester is treated with base. This is most likely to occur if we attempt to hydrolyse the P-ketoester to give a P-ketoacid using aqueous base. Note that the alcoholic base used for the Claisen reaction does not affect the ester group. 

To get the final product we need to lose the ester function. This is a standard combination of acid-catalysed ester hydrolysis followed by heating. The P-ketoacid forms a hydrogen-bonded six-membered ring that facilitates decarboxylation. 

Relatively acidic carbon acids such as malonic esters and jS-keto esters were the first class of carbanions for which reliable conditions for alkylation were developed. The reason being that these carbanions are formed using easily accessible alkoxide ions. The preparation of 2-substiuted /i-kcto esters (entries 1, 4, and 8) and 2-substituted derivatives of malonic ester (entries 2 and 7) by the methods illustrated in Scheme 1.5 are useful for the synthesis of ketones and carboxylic acids, since both /1-ketoacids and malonic acids undergo facile decarboxylation ... 

A methyl ester was formed by methanolysis of a trihalide (Equation 32) <2007S225>. Decarboxylation of the /3-ketoacid resulting from hydrolysis has also been reported (Equation 33) <1980LA1917>. A carboxylic acid substituent was reduced to aldehyde with LAH (Equation 34) <1974J(P1)2092>. Thiazine nitrogen probably participates in this reaction. 

Fig. 15 Preparation of anionic 1,3-dioxolane surfactant from ethyl esters of ketoacids...

Heating the first-obtained product in a strong acid leads to the hydrolysis of the ester. The resulting (3-ketoacid loses carbon dioxide under reaction conditions the acetal hydrolyses also reveal the free aldehyde (106-6). Aldol condensation of this last intermediate in the presence of a base with readily available rhodanine (106-7) links the two fragments. The double bond in the first-formed product is then reduced catalytically to afford darglitazone (106-8) [117]. 

If, instead of an ester, the Japp-Klingemann reaction is done with a salt of a [3-ketoacid, decarboxylation occurs and the eventual product is a 2-acyl-indole. 

Acylation of homoveratric esters 51 leads to the stable 3-alkoxy-substituted cations 52, whereas the use of homoveratric acid 51 (R = H) gives the unstable 3-acyloxy-substituted salts 53, which are easily hydrolyzed to ring-opened ketoacids 54 [70KGS(2)200]. 

Some of the best-known examples of decarboxylation in organic chemistry include the conversion of 3-ketoacids to ketones in the acetoacetic ester synthesis and the conversion of malonate derivatives to substituted carboxylic... 

A shorter reaction time (15 min) was required for the analogous conversion of alkynyl ethers, which gave the corresponding esters of a-ketoacids in an average 60% yield [18],... 

Let s examine the mechanism of the last part of the acetoacetic ester synthesis, which results in the loss of the ester group. Treatment of the /3-ketoester with aqueous base results in saponification of the ester to form, after acidification, a /3-ketoacid. The mechanism for this step was described in Chapter 19. 

An example of a reaction, first presented in Section 20.4, that falls under the pericyclic classification is the decarboxylation of /3-ketoacids produced in the malonic and acetoacetic ester syntheses ... 

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